The present invention relates to a method and a device for producing shaped ceramic bodies.
In German Published Patent Application No. 43 09 005 is discussed a method for producing multilayer hybrids from a plurality of ceramic green sheets which contain organic auxiliary agents as binders and sintering aids, and which are provided with printed circuit traces and plated-through holes. The stack of green sheets is pressed together by two porous, ceramic setter plates during sintering and removal of the binder, to ensure the least possible shrinkage and buckling within the green sheets. To achieve a simple separation between the setter plates and the multilayer hybrid after the sintering process, the setter plates are provided with a porous separating layer made, for example, of aluminum oxide which can be applied by slip casting or silk-screen printing. The organic auxiliary agents in the form of the binder or sintering additive are largely pyrolyzed during the binder removal or sintering, for example, in a hot press under axial pressure, and escape as organic bake-out products. In this context, the escape takes place, in part, via the porous setter plates or the applied porous separating layers which are gas-permeable. Damage to the ceramic sheets may result from burning out the organic auxiliary agents too quickly. Damage may result from the diffusion of the broken-up, split-off or partially-burned organic bake-out products through the setter plates. It is believed that there is a maximum portion of hydrocarbons in the oven atmosphere (to remain below the explosion limiting values) determine the speed for the duration of the binder removal and sintering process.
An object of an exemplary method of the present invention is to provide a method in which the necessary period of time for the sintering and removal of binder from the shaped ceramic bodies is markedly shortened, without, for example, exceeding the explosion limiting values in the oven atmosphere.
It is believed that the exemplary method of the present invention has the advantage that, by introducing a catalytically active substance into the pores of the porous setter plates and/or into the pores of the porous separating layers, a catalytic conversion of the gaseous bake-out products that escape when baking out the green bodies is at least partially achieved. The bake-out products are, in one exemplary embodiment, decomposition products of the organic auxiliary agents and contain hydrocarbons, among other things.
The escaping bake-out products are, in an exemplary embodiment, converted into less combustible or incombustible gases. In this manner, an exemplary method of the present invention may be used to bake out more organic auxiliary agents per unit of time than previously, without, for example, the explosion limiting values for hydrocarbons being reached in the oven atmosphere. It is believed that this results in a considerable time savings during the sintering and/or removal of the binder from the green bodies, and thus to a shortening of the oven cycles, which should mean a marked cost reduction and a substantially lower need for investment in oven installations.
Moreover, it is believed that catalytically converted, low-molecular oxidation or bake-out products diffuse more quickly through the porous setter plates and the optionally provided separating layers than unconverted, high-molecular bake-out products, which may mean a further time savings during production. According to one exemplary method and/or device of the present invention, installations for the catalytic afterburning of the waste gases carried away from the ceramic green bodies via the setter plates may be smaller.
According to one exemplary embodiment of the present invention, in addition to being introduced into the porous setter plates, the catalytically active substance may also be introduced into the porous separating layers, which is believed to bring with it advantages from the standpoint of process engineering. In an alternative exemplary embodiment, given an appropriate activity of the introduced, catalytically active substance, it may even be sufficient if the substance is only in the porous separating layers, which should lead to a markedly reduced need for these sometimes expensive materials. In the same way, for some purposes it may be sufficient if the catalytically active substance is merely introduced into the surface area of the porous setter plates or separating layers, for example, by spraying on or impregnating. This may also reduce material costs.
Thus, in one exemplary method according to the present invention, starting materials may be used which, in the course of a thermal after-treatment of the setter plates and/or the separating layers, respectively, are converted to form metallic, nano-scale particles in the pores of the setter plates and/or the separating layers.
Another exemplary embodiment involves the selection of a metallic-salt solution as the starting material for introducing the catalytically active substance. In this exemplary embodiment there may be no unwanted, in particular inorganic, residues remaining in the setter plates and/or separating layers after the thermal after-treatment.
For faster removal of gaseous bake-out and conversion products, it is believed that the setter plates may be provided with additional gas outlets arranged, in particular, parallel to the surface of the setter plates.